• In a crude processing unit we have two stages of separation (gas, oil & water) and two stages of desalter. I need to know if we should heat the crude between two separators or before the first desalter? and why?



  • Kumar N S, BPCL, nsenthilkumar152@gmail.com

    The recommended desalter temperature is between 120 and 150 oC. The higher the temperature, the better the desalting efficiency; typically, the solubility of the salt in water increases with temperature. Also, the settling or separation of water in the desalter follows Strokes's law of settling, in which an increase in temperature reduces viscosity, leading to a higher settling rate. However, high temperatures may lead to increased conductivity and higher current consumption in Desalters. Typically, desalters are designed to operate below 160 oC; this limitation is mainly due to the transformer bush design. So kindly consider these factors before deciding where to position the separator. 



  • Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

    Well, this is a very interesting question, an increase in the process temperature has two antagonic effects which need to be balanced aiming to maximize the separation and desalting efficiency. The crude oil heating will reduce the density and viscosity which will settling rates of the water droplets in the oil phase allowing a higher processing capacity of the water-oil separating system. On the other hand, the temperature increase will raise the conductivity of the crude oil, demanding a higher power consumption to promote an adequate desalting.

    Some studies point out that the adequate temperature for desalting is above 140 oC but it can be optimized according to the characteristics of processed crude oil once heavier crudes tend to present hard separation and desalting characteristics due to the lower density gap between water and crude oil. I believe that you can carry out an economic and energetic integration study aiming to heat the crude upstream the water-oil separating system to a intermediate temperature to improve the water-oil separation and   promote another heating to a higher temperature aiming to maximize the performance of desalting process considering the limitation effect over the conductivity of the crude oil. Based on the information in your question, I believe that the best location for the heat exchanger is between the separators aiming to maximize the performance of the water-oil separating system and avoid an eventual overload of the desalting system.